1. Field of the Invention
The present invention relates to a thin film magnetic head having at least an inductive-type magnetic transducer for writing, a method of manufacturing the same, and a method of forming a thin film coil.
2. Description of the Related Art
In recent years, improvement in performance of thin film magnetic heads has been sought in accordance with improvement in surface recording density of a hard disk drive. As a thin film magnetic head, a composite thin film magnetic head in which a recording head having an inductive-type magnetic transducer for writing and a reproducing head having a magnetoresistive element (hereinbelow, referred to as MR) for reading-out are stacked is widely used. MR elements include an AMR using an anisotropic magnetoresistive effect (hereinbelow, referred to as AMR) and a GMR element using giant magnetoresistive effect (hereinbelow, described as GMR). A reproducing head using the AMR element is called an AMR head or simply an MR head. A reproducing head using the GMR element is called a GMR head. The AMR head is used as a reproducing head whose surface recording density is higher than 1 gigabit per square inch. The GMR head is used as a reproducing head whose surface recording density is higher than 3 gigabits per square inch.
As methods of improving the performance of a reproducing head, there are a method of changing the material of the MR film to a material having excellent magnetoresistivity of the AMR film, GMR film, or the like, and a method of making the pattern width of the MR film, especially, the MR height proper, and the like. The MR height is the length (height) from the end part on the air bearing surface side of the MR element to the end part on the opposite side and is controlled by the polishing amount at the time of processing the air bearing surface. The air bearing surface is a surface of a thin film magnetic head, which faces a magnetic recording medium, and is also called a track surface.
On the other hand, in accordance with the improvement in performance of a reproducing head, the improvement in performance of a recording head is also required. One of the factors of determining the performance of a recording head is the throat height (TH). The throat height is the length (height) of a magnetic pole part extending from the air bearing surface to the edge of an insulating layer which electrically isolates a thin film coil for generating a magnetic flux. In order to improve the performance of a recording head, reduction in the throat height is desired. The throat height is also controlled by the polishing amount at the time of processing the air bearing surface.
Further, in order to improve the performance of the recording head, it is proposed to shorten the length (hereinbelow, called a magnetic path length) of the part sandwiching the thin film coil of a bottom pole and a top pole formed while sandwiching a write gap.
With reference to FIGS. 16A and 16B through FIG. 21, as an example of a method of manufacturing a conventional thin film magnetic head, an example of a method of manufacturing a composite thin film magnetic head will be described. FIGS. 16A through 20A are sections each of which is perpendicular to the air bearing surface in a main manufacturing process. FIGS. 16B through 20B are sections each of which is parallel to the air bearing surface in a main manufacturing process. FIG. 21 illustrates a plane structure of a completed composite thin film magnetic head.
First, as shown in FIGS. 16A and 16B, an insulating layer 102 made of, for example, alumina (aluminium oxide, Al.sub.2 O.sub.3) is formed in a thickness of about 5 to 10 .mu.m on a substrate 101 made of, for example, altic (Al.sub.2 O.sub.3.TiC). Subsequently, a bottom shield layer 103 for a reproducing head made of, for example, permalloy (NiFe) is formed on the insulating layer 102. For example, alumina is then deposited in a thickness of 100 to 200 nm on the bottom shield layer 103 to form a shield gap film 104. An MR film 105 for constructing an MR element for reproducing is formed in a thickness of tens of nanometers on the shield gap film 104 and is formed in a desired shape by high-precision photolithography. Then a lead terminal layer 106 for the MR film 105 is formed by lift-off method. A shield gap film 107 is formed on the shield gap film 104, the MR film 105 and the lead terminal layer 106, and the MR film 105 and the lead terminal layer 106 are embedded in the shield gap films 104 and 107. An top shield-cum-bottom pole (hereinbelow, referred to as bottom pole) 108 with 3 .mu.m thick made of a magnetic material such as permalloy (NiFe) used for both the reproducing head and the recording head is formed on the shield gap film 107.
On the bottom pole 108, a write gap layer 109 with 200 nm thick made of as an insulating film such as an alumina film is formed. Further, the write gap layer 109 is patterned by photolithography and an opening 109a for connecting the top pole and the bottom pole is formed. Subsequently, a pole tip 110 is formed by using a magnetic material such as permalloy (NiFe) or iron nitride (FeN) by plating and a connecting part pattern 110a for connecting the top pole and the bottom pole is formed. By the connecting part pattern 110a, the bottom pole 108 and a top pole layer 116 which will be described hereinlater are connected and formation of a through hole after a CMP (Chemical Mechanical Polishing) process which will be described hereinlater is facilitated.
Subsequently, as shown in FIGS. 17A and 17B, the pole tip 110 is used as a mask and the write gap layer 109 and the bottom pole 108 are etched about 0.3 to 0.5 .mu.m by ion milling. Etching is performed to the bottom pole 108 and a trim structure is obtained, thereby preventing the effective write track width from being expanded (that is, the expansion of a magnetic flux in the bottom pole is suppressed when data is being written). Subsequently, an insulating layer 111 made of, for example, alumina with a thickness of about 3 .mu.m is formed on the whole surface and then the whole surface is planarized by CMP.
As shown in FIGS. 18A and 18B, a thin film coil 112 as the first layer for an inductive recording head made of, for example, copper (Cu) is selectively formed on the insulating layer 111 by plating or the like. Simultaneously, a pattern 112a for connecting coils is formed integrally with the thin film coil 112 on the insulating layer 111 rearward of the connecting part pattern 110a. A photoresist film 113 is formed in a predetermined pattern by high-precision photolithography so as to cover the insulating layer 111, thin film coil 112 and coil connecting pattern 112a. The photoresist film 113 is patterned so as to form openings 113a and 113b for exposing the top surface of each of the connecting part pattern 110a and the coil connecting pattern 112a. Subsequently, heat treatment is performed at a predetermined temperature for planarizing the photoresist film 113 and for insulating between the turns of the thin film coil 112.
As shown in FIGS. 19A and 19B, a thin film coil 114 as the second layer is selectively formed on the photoresist film 113. Simultaneously, a pattern 114a for connecting coils to be electrically connected to the coil connecting pattern 112a is formed integrally with the thin film coil 114 on the opening 113b of the photoresist film 113. Subsequently, a photoresist film 115 is formed so as to cover the thin film coil 114 as the second layer and the coil connecting pattern 114a. Further, heat treatment is performed at a predetermined temperature for planarizing the photoresist film 115 and for insulating between the turns of the thin film coil 114.
As shown in FIGS. 20A and 20B, an top yoke-cum-top pole layer (hereinbelow, referred to as top pole layer) 116 made of a magnetic material such as permalloy for the recording head is selectively formed on the pole tip 110 and the photo resist films 113 and 115. The top pole layer 116 is in contact with and magnetically coupled to the bottom pole 108 via the connecting part pattern 110a in the opening 113a in the area (right area in the diagram) surrounded by the thin film coils 112 and 114. Subsequently, an overcoat layer 117 made of, for example, alumina is formed on the top pole layer 116. Finally, by performing a mechanical process of a slider, the track surface (air bearing surface) 118 of the recording head and reproducing head is formed, thereby completing a thin film magnetic head.
In FIGS. 20A and 20B, and FIG. 21, the coil connecting pattern 112a is connected to the inner circumferential end of the thin film coil 112 of the first layer and the coil connecting pattern 114a is connected to the inner circumferential end of the thin film coil 114 of the second layer. In the diagrams, however, the connected parts are omitted. In the case of such a connecting mode, the winding (turning) direction of the coil, that is, the direction of a current is, for example, as follows. Specifically, when the outer circumferential end of the thin film coil 112 of the first layer is used as a start point, the current flows in one direction (for example, clockwise direction) in accordance with the order of the outer circumferential end of the thin film coil 112, the inner circumferential end of the thin film coil 112, the coil connecting pattern 112a, the coil connecting pattern 114a, the inner circumferential end of the thin film coil 114, and the outer circumferential end of the thin film coil 114.
In the actual manufacture of a thin film magnetic head, a wafer on which a number of the above structures are formed is divided into bars on which a number of thin film magnetic heads are arranged. The sides of the bars are polished, thereby obtaining the air bearing surface 118. In the process of forming the air bearing surface 118, the MR film 105 is also polished and a composite thin film magnetic head having a desired throat height and MR height is obtained. Further, in a actual thin film magnetic head, contact pads to be electrically connected to the thin film coils 112 and 114, and the MR film 105 are formed. In the above diagrams, however, they are omitted.
In FIGS. 20A and 21, TH indicates the throat height. In FIGS. 20A and 20B, MR-H indicates the MR height, P2W indicates the track (pole) width, the angle .theta. indicates an apex angle formed between the straight line connecting the corners of sides on the track face sides of the photoresist films 113 and 115, and the top surface of the top pole layer 116, and LM indicates the magnetic path length. All of the parameters are important as factors determining the performance of a thin film magnetic head.
The conventional composite thin film magnetic head formed as mentioned above has the following problems especially in reducing the size of the recording head.
The magnetic path length LM is the length of the bottom pole and the top pole in the part surrounding the thin film coils as described above. It is generally known that by shortening the magnetic path length LM, flux rise time, non-linear transition shift (NLTS) characteristic, over write characteristic, and the like of a inductive-type thin film magnetic head can be improved. The flux rise time is the time from the instant when the current is flowed to the thin film coil until the flux density in a magnetic circuit consist of the bottom and top poles reaches a predetermined level and exerts an influence on the high frequency characteristics at the time of recording. The non-linear transition shift is a phenomenon that the position of transition (part where the magnetizing direction is inverted) in which data is newly recorded is shifted by the interaction between the magnetic flux from a magnetic domain to which the recording is performed just before that and the magnetic flux of the recording head. The non-linear transition shift exerts an influence on the accuracy of the data recording position and, moreover, the surface density characteristic at the time of recording.
In order to reduce the magnetic path length LM, it is sufficient to make the pitch of the thin film coil small, but there is the limitation. Usually, a method of stacking two thin film coils sandwiching an insulating layer as shown in FIGS. 20A and 20B is employed. In this case, when the photoresist layer is used as an insulating layer as in the above example, the opening 113b for connecting the thin film coil 112 of the first layer and the thin film coil 114 of the second layer can be simultaneously formed upon patterning in the photolithography process.
Since the photoresist layer shows flowability by being heated, however, there is an inconvenience such that the end position of the photoresist layer (TH zero position as a reference of the throat height) changes in a heat treatment process. It is therefore considered to form the insulating layer between the thin film coils (hereinbelow, simply called an insulating layer between coils) by using an inorganic insulating material, instead of a photoresist as an organic material. In this case, however, a process of forming an opening for connecting the two thin film coils in the insulating layer between the coils is separately needed. Consequently, there has been a problem such that the manufacturing process is complicated.